(a) The Field of the Invention
The present invention relates to a process and a device for interlacing multifilament yarns.
(b) The Prior Art
A process is known for imparting a certain degree of coherency to yarns constituted by a plurality of substantially parallel filaments--whereby it is meant that the yarn is without twist or has a very low twist--so that they may be employed in weaving and typically for making warps. The known process consists essentially in directing an air jet onto the yarn which travels in a straight line while limiting the freedom of motion of the yarn and containing and deflecting the air stream after contact with the yarn, to an extent and in a manner which are different from case to case.
Typically such processes are carried out by means of devices which comprise a nozzle and a yarn guide and control organ. It is customary in the art improperly to call both those organs together "nozzle", while they should be considered as two distinct elements even when they are formed in a single body. The nozzle proper is of course essentially an air outlet orifice fed with air under pressure through an air feed passage or channel. The yarn guide and control organ, on the other hand, embodies either yarn guide devices or surfaces which limit the yarn motion in the direction of the air jet axis and/or in a direction perpendicular thereto, and often also comprises curved surfaces which are stricken by and deflect the air jet. In some devices, the nozzle and the guide and control organ are clearly distinguished and this latter sometimes merely consists of a surface, e.g. cylindrical, which limits the motion of the yarn in the direction of the air jet axis and lateraly deflects the flow lines of the air jet (see e.g. Italian Pat. No. 700.695). Other devices, e.g. that of U.S. Pat. No. 2,985,995, and others described in a series of patents which are developments and modifications of this latter, comprise a guide and control organ the functional portion of which is a cylindrical channel through which the yarn passes, while the nozzle is nothing but a bore having an axis perpendicular to the axis of the channel, and from which the air jet enters into the channel and therein acquires swirling motions. In nozzles of this type, it is usual that both the yarn passage channel and the air feed channel be formed in a single body, which justifies the fact that the whole device is called "nozzle".
The known processes and devices make it possible to interlace essentially parallel multifilament yarns at high speeds and with good efficiencies. The degree of coherency is measured, e.g., as described in the cited U.S. Pat. No. 2,985,995, by passing a hook carrying a standard weight between the filaments of the yarn and registering the number of times it is stopped while traversing a given length, or in other words by measuring the number of knots or more exactly "pseudo-knots" which the yarn has acquired. It is obvious that in such measurements the morphology of the yarn is at least temporarily modified by the measuring instrument, and the quantitative results they furnish have a comparison value but do not define or express the intimate structure of the interlaced yarn.
However, such known processes and devices involve a rather substantial consumption of compressed air which increases the cost of the final product. They have other drawbacks as well, different from case to case, e.g. a limitation of the range of yarns which may be processed, difficulties of starting the yarn in the device, sensitivity to tension variations, difficulty of regulation, complexity of construction and control, and so forth. Attempts to eliminate these drawbacks have not been wholly successful.
The present invention completely eliminates such disadvantages, and substantially improves the efficiency and the economy of the yarn interlacing operation, thanks to a process and a device which are based on a new principle, while remaining in the class of pneumatic yarn treatments and devices.